Why Did Grogu Leave Luke Skywalker?

After Grogu chose to be with the Mandalorian over becoming a Jedi, Luke probably didn't know what to do next. Grogu was going to be the first student that Luke ever had, and after he decided to leave, the Jedi Master likely doubted his ability to actually train a new generation of Force-users.

Is Grogu done with Luke?

Audiences were never shown what transpired after Grogu was presented with his choice by Luke, so there may well be more to the situation. In the long run, it doesn't seem likely that he'll rejoin Skywalker Academy; Grogu is being set up to be the next Mandalorian Jedi, so he'll remain by Din's side for years to come.

How long did Luke train Grogu?

Grogu's brief tutelage under Luke Skywalker ended in The Book of Boba Fett, and it'd be six years before Luke would begin training his official first student, Ben Solo.